Integrated freewheeling diode and extraction device

ABSTRACT

A Freewheeling Diode of any kind (Fast Recovery Diode, Schottky Barrier Diode or other variants) is integrated with a Forced Extraction Device and in this way two entirely different functions—the Free-Wheeling function and the Forced Extraction function are combined in one device, simplifying the circuit and reducing the number of components. The FWD part of the integrated device is standard in the industry, but the Forced Extraction Device is made using a lateral or vertical PMOS with a votage capability between a control input and the output terminals that is as high or higher than the rating voltage of the Main Switch that will be used together with the FWD.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/496,658, filed Oct. 7, 2021, which is a non-provisional of and claimsbenefit to U.S. provisional patent application No. 63/093,701, filedOct. 19, 2020, entitled SEMICONDUCTOR STRUCTURE HAVING A FORCEDEXTRACTION DEVICE, the disclosure of which is incorporated herein byreference in its entirety. This application is also related to U.S.patent application Ser. No. 17/339,832, filed Jun. 4, 2021, entitledPOWER SEMICONDUCTOR DEVICE WITH FORCED CARRIER EXTRACTION AND METHOD OFMANUFACTURE, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to semiconductor devices, and, moreparticularly, to a semiconductor structure that includes a FreewheelingDiode coupled to a forced carrier Extraction Device that improves theswitching speed of a Main Switch for which the turn-off process dependson the recombination speed of charge carriers.

BACKGROUND

The previously incorporated U.S. patent application Ser. No. 17/339,832describes problems with long turn-off times in power semiconductorswitches and a solution that uses a forced carrier Extraction Device.Some power semiconductor devices that carry relatively large amounts ofcurrent include a Freewheeling Diode (FWD), especially those thatoperate on inductive loads. In power circuits like push-pull,half-bridge or full-bridge modules, the Freewheeling Diode is connectedin parallel to the main semiconductor switch. Some power switches, likeMosfets, have a “built in” diode, which can be used as a FreewheelingDiode. In such cases, special process steps are used to shorten thereverse recovery time and lower the reverse recovery charge of the FWD,as this charge contributes to the turn-on switching energy of the MainSwitch.

Insulated Gate Bi-Polar Transistors (IGBTs) are widely used for a broadrange of power semiconductors since their features are well suited forsuch roles. IGBTs include a built-in diode, but the built-in diodecannot be used as a FWD because of the P-type injector layer, whichcauses the built-in diode of the IGBT on the backside of the IGBT tohave an orientation opposite that of a Mosfet. The diode in an IGBT isformed at the intersection of the P-wells and N-type drift layer, forinstance, or at the intersection of an N-well for a P-type IGBT. Theinjector layer of the IGBT provides the conductivity modulation of thedrift region while the IGBT is conducting, which makes the IGBT such awell-performing device from an on-conduction point of view. But thissame injector layer prevents the built-in diode in an IGBT from actingas an FWD, which is why nearly all IGBTs are equipped with a separateFWD in most power applications.

Recently, Silicon Carbide Schottky Barrier Diodes (SiC SBDs) have beenreplacing Silicon FWDs in commercial products. An SBD formed on SiC hasa lower forward voltage and no reverse recovery charge, and thereforeits contribution to the turn-on energy loss of the Main Switch, such aswhen an IGBT is used for the Main Switch, is due only to the chargestored in the depletion region of the SBD.

Another effect of the existence of the injector layer opposite to theMosfet makes the turn-off process of a Main Switch that employsconductivity modulation, such as an IGBT, very slow, due to the need ofthe injected carriers to “disappear” through recombination when the IGBTturns off.

Special process steps that control the level of injection or therecombination rate are widely used to speed up the turn-off time ofpower semiconductors that use conductivity modulation. Providing such aswitch, such as an IGBT, with an ability or structure to remove excesscharge in the drift region and therefore lower the turn-off energy ofthe power semiconductor, is a worthwhile goal.

State-of-the-art IGBTs lack the means to access the region where thecarriers contributing to the conductivity modulation recombine.Extraction Plugs, which are described in detail in the incorporated '832application, may be formed or placed inside the Main Switch, such as anIGBT, such that the electrical performance of the Main Switch is notdegraded in any way. Although such Extraction Plugs may speed up a powersemiconductor switch when coupled to an Extraction Device to removecharge in the drift region during the turn-off process of the switch,forming the Extraction Device itself may involve extra process stepscompared to forming the IGBT itself.

Embodiments of the disclosure address these and other limitations of theprior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual schematic diagram of a switch having anExtraction terminal, connected to a voltage-controlled ExtractionDevice, according to embodiments of this disclosure.

FIG. 2 is a schematic diagram of a complementary IGBT having aninjecting PNP transistor, as well as a P-channel MOSFET, and anN-channel MOSFET coupled in series, according to embodiments of thedisclosure.

FIG. 3 is a simplified schematic diagram illustrating an IGBT switchingdevice, having emitter, collector, and gate terminals, and furtherillustrating an Extraction Plug connection, to which an ExtractionDevice may be connected, according to embodiments of the disclosure.

FIG. 4 is a schematic of a known voltage-controlled Main Switch, such asan IGBT, having a free-wheeling diode connected in parallel to theswitch.

FIG. 5 is a schematic diagram illustrating a Main Switch, a FreewheelingDiode, and an Extraction Device, according to embodiments of theinvention.

FIG. 6 is a cross-sectional diagram of a Freewheeling Diode and anExtraction Device, according to embodiments of the invention.

FIG. 7 is a cross-sectional diagram illustrating a Freewheeling Diode,high-voltage termination, and a multi-cell PMOS formed on asemiconductor substrate, according to embodiments of the invention.

FIG. 8 is a cross-sectional diagram of a lateral PMOS Extraction Deviceand a high voltage capacitor according to embodiments of the invention.

FIG. 9 is a cross-sectional diagram of a vertical PMOS Extraction Deviceand a high voltage capacitor according to embodiments of the invention.

FIG. 10 is a top layout view of an integrated FWD with an ExtractionDevice, placed outside of the high voltage termination of the FWD,according to embodiments of the invention.

FIG. 11 is a top layout view of an integrated FWD with an ExtractionDevice, interspaced in the active area of the die, according toembodiments of the invention.

FIG. 12 is a top layout view of a voltage controlled Main Switch havingan output on the backside of the die, according to embodiments of theinvention.

FIG. 13 is a top assembly view of a voltage controlled Main Switchhaving Extraction Plugs formed around an edge of the die, according toembodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure relates to the field of power semiconductors withconductivity modulation, like IGBTs and its variants, which arestructured or used to switch inductive loads. When switching inductiveloads, a Freewheeling Diode is commonly used when the switching device,like the IGBT, has to commutate On and Off current through aninductance. Thus, although IGBTs remain an excellent choice for thosesemiconductor devices carrying relatively large amounts of current, socalled power devices, the slow switching speeds caused by the slowrecombination of minority carriers in conductivity-modulation bipolardevices after switching off continues to inhibit their performance.Including Extraction Plugs and an Extraction Device in a three terminaldevice that uses conductivity modulation can greatly improve itsswitching speed, as described below.

Benefits of including an Extraction Device in conjunction with a powersemiconductor device are described with reference to FIGS. 1-3 .Benefits of including FWDs with power semiconductor devices that alsoinclude an Extraction Device are described with reference to FIGS. 4-13.

FIG. 1 is a conceptual schematic diagram of a combined device 100 thatgenerally includes a Main Switch 110 coupled to an Extraction Device120. The device 100 further includes one or more Extraction Plugs 130formed in the drift layer of the Main Switch 110. Extraction Plugs arefully described in the previously incorporated U.S. patent applicationSer. No. 17/339,832. In general, Extraction Plugs may be formed indevices that use conductivity modulation to provide access to a driftlayer of the device. The Extraction Plugs 130 are formed and placed sothat they do not degrade, in any way, the performance of the structure100, especially its blocking voltage. An Extraction Device 120, alsodescribed in the '832 application, turns on when the Main Switch 110turns off. If the Main Switch is embodied by a device that usesconductivity modulation, such as an IGBT, the Extraction Device 120works to remove charge carriers left over in the bulk region when theMain Switch 110 turns off through the Extraction Plug 130 of the MainSwitch. The forced Extraction Device 120 is preferably voltagecontrolled, and its blocking voltage between terminals is generally thesame or higher than the blocking voltage of the Main Switch 110.

The structure 100 of FIG. 1 may be structured as a three-terminaldevice. The structure 100 includes an input terminal coupled to an input112 of the Main Switch 110 and to an input 122 of the Extraction Device120, and an output terminal 126 coupled to an output of the ExtractionDevice 120. The structure 100 further includes a ground terminal 114coupled to the Main Switch 110. Because the inputs 112, 122 of the MainSwitch 110 and Extraction Device 120 are tied together, the input signaldriving the input 112 of the Main Switch 110 also drives the input 122of the Extraction Device 120.

The Extraction Device 120 may be integrated on the same die as the MainSwitch 110, or it may be a discrete device formed on a separatesemiconductor substrate that is electrically coupled to the Main Switch.In some embodiments the semiconductor substrate for the Main Switch anda semiconductor substrate for the Extraction Device 120 may be separatesubstrates but assembled together in a single module or even in a singlepackage.

The structure 100 of FIG. 1 conceptually operates as indicated as inTable 1:

TABLE 1 Operational States of Main Device and Extraction Device TurnTurn Input-Ground Output-Ground Device/State On Off Voltage Voltage MainDevice On Off Low High Extraction Device OFF On High Low

In operation, when the Main Switch 110 is ON, the Extraction Device 120is OFF, and vice-versa. In device operation, i.e., when the Main Switch110 is conducting, the Extraction Device 120 does not interfere oraffect the operation of the Main Switch 110. In other words, theoperating parameters of a Main Switch 110 coupled to the ExtractionDevice 120 are the same or similar as a Main Switch that is not coupledto an Extraction Device. The Main Switch 110 has a low breakdown voltagebetween the input and ground terminals, but a relatively high breakdownvoltage between the output and ground terminals. Conversely, theExtraction Device 120 has a high breakdown voltage between its input andground terminals, and a relatively low breakdown voltage between theground and the output terminals.

FIG. 2 is a schematic diagram of a circuit 200 including components thatmay be used to form an example embodiment 200 that functions as thestructure 100 of FIG. 1 . The circuit 200 includes an IGBT Main Switch,which is formed of a PNP transistor 250 as an injector and an N-channelMosfet 270 that drives the PNP transistor. A P-channel Mosfet 260functions as the Extraction Device 120 of FIG. 1 . The Mosfets 260 and270 are coupled in series. The device 200 may be integrated on a singlesemiconductor die. In other embodiments, as described above, theP-Channel Mosfet 260 may be formed on a separate semiconductor die andelectrically connected to the N-Channel Mosfet 270. Internal componentsof the IGBT Main Switch further include a collector 216, and an emitter214. The P-Channel Mosfet 260, which operates as the Extraction Device,includes a source 224 and a drain 226. Since the output terminal of thedevice 200, in this configuration, is coupled to both the collector 216of the IGBT and the drain 226 of the P-Channel Mosfet 260, it is labeledas Output/Drain/Collector. Similarly, the ground terminal is coupled tothe emitter 214 of the IGBT and the source of the N-Channel Mosfet 270,the ground terminal is labeled Ground/Source/Emitter. Finally, since theinput terminal of the device 200 is coupled to the gates of both theN-Channel Mosfet 270 and the P-Channel Mosfet 260, the input terminal islabeled Input/Gate. Although it is not separately shown on the schematicdiagram of the circuit 200, an Extraction Plug for the IGBT would becoupled to the base of the PNP transistor 250, which is in the driftregion of the IGBT, and is labeled as reference 280. Importantly, theExtraction Plug, or reference 280, is electrically coupled to a sourceof the P-Channel Mosfet 260.

In operation of the device 200, when the Input/gate voltage is HIGH, thebase of the PNP 250 transistor is connected to a ground at the source ofthe MOSFET 270, while the device 200 is conducting. Then, when theInput/gate voltage goes LOW, to turn off the device 200, the N-channelMOSFET 270 turns OFF, while the P-channel MOSFET 260 turns ON. TheP-Channel MOSFET 260 turning ON provides a path for excess charge to beremoved from the drift region 280 from the source of the P-ChannelMosfet 260 to the drain of the P-Channel Mosfet, which is coupled to theoutput of the device 200. The P-Channel MOSFET 260 is formed so that,when the gate voltage is HIGH, the P-Channel MOSFET 260 is OFF, andturns on when the gate voltage goes LOW. At low Vgs voltages of theN-Channel Mosfet 270, when the Main Switch (IGBT) turns OFF, theP-Channel MOSFET 260 operates similar to that of a resistor, with itsdrain coupled to the positively bias on the collector 216 of the PNP250. Therefore, electrons are pulled toward the positively biased drainelectrode of the P-Channel MOSFET 260, and charge is removed from thedrift region 280 at a relatively constant rate. The P-Channel MOSFET 260provides a path for the charge, carried by electrons, to be removed fromthe drift layer 280 through the positively charged drain. Recall thatone of the main problems for conventional IGBT devices to switch offquickly is that there is no access to the drain of the Mosfet. Instead,the Extraction Device, which here is the P-channel MOSFET 260, extractsexcess carriers relatively quickly from the bulk drift area 280 of theIGBT by conducting them to the collector through the P-channel MOSFET260. This action of removing the excess charge carriers when the IGBTturns off significantly decreases the turn-off time of the IGBT.

The aforementioned Extraction Plugs, or merely plugs, are used toprovide access to areas of the bulk semiconductor in conductivitymodulation devices. These Extraction Plugs, in turn, may be coupled tothe source (i.e, the input or extraction terminal) of an ExtractionDevice to remove the excess carriers from the conductivity modulationdevice when the conductivity modulation device is being turned off. Thisgreatly reduces the turn-off time of the conductivity modulation device.Further details of the structure of the Extraction Plugs may be obtainedfrom the '832 application, although embodiments of the invention areapplicable to other forms of Extraction Plugs providing the samefunction as that described herein.

FIG. 3 is a simple schematic diagram illustrating an IGBT switchingdevice 300, having emitter, collector, and gate terminals, and furtherillustrating an Extraction Plug terminal, also called an ExtractionTerminal, to which an Extraction Device may be connected. This schematicdiagram neatly illustrates the concepts of including one or moreExtraction Plugs in the drift region of an IGBT, which, as describedabove, facilitates the removal of carriers during forced carrierextraction from the drift region through the Extraction Plugs andfurther through the Extraction Device during turn-off of the MainSwitch. The Extraction Plug terminal is electrically connected to theExtraction Plug or Plugs in the IGBT. In application, the ExtractionPlug terminal of the IGBT switching device 300 may be further coupled toan Extraction Device, as detailed below. In embodiments where theExtraction Plug and Extraction Device are formed on the samesemiconductor substrate, it is not strictly necessary that theExtraction Plug be coupled to an output terminal. In other embodiments,where the Extraction Plug and Extraction Device are formed on differentsubstrates, the Extraction Plug may be coupled to an Extraction PlugTerminal, which, in turn, may be coupled to an Extraction Device locatedon a different substrate. In this way, the process steps for forming anIGBT having an Extraction Plugs may be optimized separately from theprocess steps for forming an IGBT.

Further, recall from above that power switching devices that driveinductive loads nearly always include a Freewheeling Diode (FWD) toprotect the switch from over voltage as the switch turns off and themagnetic field around the inductive load collapses. To protect againstdamage caused by the inductor, a protective FWD is coupled in parallelto the switch. FIG. 4 is a schematic of a known voltage-controlled MainSwitch 10, such as an IGBT, having an FWD 12 connected in parallel tothe switch. As described above, some power semiconductor devices thatcarry relatively large amounts of current include an FWD, especiallythose that operate on inductive loads. In power circuits like push pull,half-bridge or full-bridge modules, the FWD is connected in parallel tothe main semiconductor switch. With reference to FIG. 4 , the IGBT 10 isa bipolar semiconductor device used for carrying relatively largecurrent loads. The IGBT 10 includes emitter, collector, and gateterminals, which function as the input, output, and gate terminals ofthe switch. The FWD 12 is coupled in parallel to the IGBT, with oneterminal of the FWD coupled to the collector and the other terminalcoupled to the emitter. In circuits that drive inductive loads, the FWD12 shunts current from the inductive load across the IGBT 10 as the IGBTturns off, and also limits voltage across the IGBT. Otherwise, thecurrent generated by the collapse of the magnetic field around theinductor would be applied directly to the IGBT 10, which would likelycause damage. In this way the FWD 12 acts as a protection device for theswitch 10. Also, the FWD 12 is designed and fabricated to withstand thefull rated voltage of the Main Switch 10, including the avalancherating, or it has to be implemented with a higher blocking voltage thanthe Main Switch.

FIG. 5 is a schematic diagram illustrating a system 500 that includes aMain Switch 510 having an Extraction Plug electrode 512, an FWD 520, andan Extraction Device 530, according to embodiments of the invention.Although all of the components illustrated in FIG. 5 may be integratedon a single die, it is possible, and perhaps preferable, that the FWD520 and an Extraction Device 530 are packaged in a separate device 550,which is electrically connected to the Main Switch 510. Also, the MainSwitch 510 may be a one semiconductor die, and the separate device 550,including the FWD 520 and an Extraction Device 530, is formed on anothersemiconductor die, but both the semiconductor dies are together in asingle semiconductor module or package. More details and discussion ofpossible layouts is given below.

System 500 illustrates a three-terminal device capable of drivinginductive loads, since the IGBT Main Switch 510 is electrically coupledto the FWD 520, even though the diode 520 may be formed on a substrateseparate from the IGBT Main Switch 510. Further, since the turn-off timeof an IGBT is shortened by coupling an Extraction Device 530 to theExtraction Plug 512 of the IGBT 510, including an Extraction Device 530in the system 500 provides the extraction function when the IGBT 510turns off. Therefore, it may be convenient to produce the IGBT MainSwitch 510 with an Extraction Plug terminal 512 separately from a devicethat includes both an FWD as well as an Extraction Device, such as thedevice 530. Thus the system 500 may form a single package or moduleincluding one component having the IGBT Main Switch 510 and havinganother component 550, which includes the FWD 520 and the ExtractionDevice 530. Electrical connections are made within the system 500 asillustrated in FIG. 5 . For instance, a gate of the IGBT Main Switch 510is electrically coupled to an input of the Extraction Device 530. TheExtraction Plug terminal 512 of the IGBT Main Switch 510 is electricallycoupled to an extraction input 532 of the Extraction Device 530. Acollector of the IGBT Main Switch 510 is coupled to an output of theExtraction Device 530. To finish the connections, a cathode of the FWD520 is coupled to a collector of the IGBT Main Switch 510, and the anodeof the FWD 520 is coupled to an emitter of the IGBT Main Switch 510.

If the system 500 is created in a discrete package 560, it could be athree-terminal device with an input control terminal 562, a groundterminal 564, and an output terminal 566. Such a package 560 includes anIGBT 510 or Main Switch having an Extraction Plug terminal 512 that iscoupled to a component 550. The component 550 includes an FWD 520 and anExtraction Device 530. This package 560 includes all of the componentsfor a power device for driving an inductive load having a shortenedturn-off time compared to typical IGBTs. In detail, the FWD 520 iseffectively mandatory for any power switch operating with an inductiveload. Embodiments of the invention further include the Extraction Device530 to shorten the turn-off time of the voltage-controlled switch devicewith conductivity modulation 510. Although the Main Switch 510 isillustrated as being an IGBT, embodiments of the invention extend to anyvoltage-controlled switch device with conductivity modulation.

FIG. 6 is a cross-sectional diagram of an integrated device 600including an FWD 610 and an Extraction Device 620 produced on a samesemiconductor substrate, according to embodiments of the invention. Inthis example, the FWD 610 is a merged PN-Schottky structure. But, theFWD 610 may be any of several different types of FWDs. For example, theFWD 610 may be a PIN (p-type and n-type materials separated by aninsulator) diode, and may or may not include materials for shorteningcarrier lifetimes, such as gold or platinum diffusions, electron orproton irradiations, etc. The FWD 610 may also be a Fast Recovery Diode,for example. Although the FWD 610 and the Extraction Device 620 of theintegrated device 600 are formed on the same semiconductor die, they maybe separated by a deep trench 640, which may be formed using standardfabrication techniques. The deep trench 640 separates the cathode of theFWD 520 (FIG. 5 ) from the substrate of the lateral PMOS in theExtraction Device 530. Such separation allows each device to operatevirtually independent from one another. It is not necessary that the FWD610 and the Extraction Device 620 be formed on the same die. In otherembodiments the FWD 610 and the Extraction Device 620 may beelectrically coupled to one another but formed on separate semiconductordies. In the illustrated embodiment, the lateral PMOS Extraction Device620 includes a thick gate oxide 105. The Extraction Device 620 is also“counter doped” at the surface of the semiconductor to create conditionsfor a suitable turn-on voltage, Vth. As represented in this crosssection of FIG. 6 , the FWD 610 and the PMOS Extraction Device 620structures could be formed and interspaced in the active area of thedie. The device 600 is an example of the type of structure that couldmake the component 550 part of the device 500 of FIG. 5 .

Other structures in the integrated device 600 are conventional, such asa polysilicon gate 103, front metal 106, passivation layer 108,substrate 150, such as SiC or other wide bandgap material, N-type driftregion 151, P-Wells 160, Schottky Metal 165, and counter-doped region170.

FIG. 7 is a cross-sectional diagram of a device 700 illustrating an FWD710, high-voltage termination 750, and a multi-cell PMOS ExtractionDevice 720 formed on any type of semiconductor, such as Silicon, SiC,wide-bandgap material, etc., according to embodiments of the invention.The placement of the Extraction Device 720 in the illustrated embodimentof FIG. 7 is outside of the High Voltage Termination 750 of the FWD 710,but this placement is not mandatory. The P-Wells 101 of the FWD 710 andExtraction Device 720 can very well operate together to provide ablocking voltage needed for the FWD. Other conventional components ofthe device 700 not referred to above include a gate 202, source 203, anddrain 204 of the PMOS transistors in the Extraction Device 720.

FIG. 8 is a cross-sectional diagram of a lateral PMOS Extraction Device800 that includes a PMOS transistor 810 coupled to a high voltagecapacitor 820, according to embodiments of the invention. The capacitor820 includes electrodes 822 separated by an insulating or dielectriclayer 824. The PMOS transistor 810 includes a thin gate oxide 812. Insome instances the thin gate oxide 812 is easier to produce than a thickgate oxide, used in previous examples, so the thin gate oxide may bepreferable. The high voltage capacitor 820 is series coupled to thebuilt-in capacitance of the thin gate oxide 812. As described above,when a PMOS transistor is used as the Extraction Device, the ExtractionDevice does not have any substantive function during the DC operation ofthe Main Switch, i.e., while the Main Switch is fully off or fully on.This means the Extraction Device 800 is OFF when the Main Switch isturned ON and it is ON when the Main Switch gets turned OFF. Given thesecharacteristics, it is possible for an external capacitor with arelatively high voltage rating to be used to seamlessly protect the gateoxide of the PMOS Extraction Device, even when, such as in theExtraction Device 800, it has a thin gate oxide. This series circuitconfiguration is possible because the PMOS Extraction Device 800operates only during the switching on and off of the Main Device (notillustrated in FIG. 8 ) to which it is coupled, and the switchingcontrol signals also cause the turn-on and turn-off of the PMOStransistor 810 in a seamless way. Further, by using a high-voltageexternal capacitor 820 in series with the capacitor formed by apolysilicon gate and the gate oxide 812 of the lateral PMOS 810, thetotal capacitance of the series connection of these two capacitances canbe tailored to adjust the voltage spikes of the gate signal. Thisprotection is important, especially in the case when the Main Switch ismade on wide bandgap semiconductors, for which the gate oxides are verythin and therefore very sensitive to voltage spikes. The capacitance ofthe series connection of the capacitance of the gate oxide 812 of thePMOS 810 and the capacitor 820 itself may range from 1 pF to 800 pF, andmore preferably from 1 pF to 100 pF. Of course, the specific values ofthe capacitance of the series connection will be implementationspecific. The Extraction Device 800 is an example type of device thatmay be present in the device 550 and used for the Extraction Device 530of FIG. 5 .

FIG. 9 is a cross-sectional diagram of a vertical PMOS Extraction Device900, including a vertical PMOS transistor 910. The PMOS transistor 910may be made on any type of semiconductor material. The PMOS transistor910 in this embodiment has a thick gate oxide 105, which provides a highvoltage rating for the PMOS transistor 910, exceeding that of a MainSwitch to which it is connected. Also, the Extraction Device 900includes a high-voltage rated capacitor 920 that is connected in serieswith the Gate-Drain capacitance of the vertical PMOS transistor 910. Thecapacitor 920 is formed of conductive plates 922 separated by aninsulator 924. Even though in this illustration the high voltagecapacitor 920 has similar dimensions as does the PMOS transistor 910,such as the Poly Gate Width of the vertical PMOS 910, in actuality, thehigh voltage capacitor 920 can be placed anywhere on the top of the PMOSdie, or outside of it and properly wire-bonded to the control electrodeof the Extraction Device.

Thus, the embodiments of the Extraction Devices illustrated in FIGS. 8and 9 illustrate various options that may be used in implementing theExtraction Device, such as the Extraction Device 530 of FIG. 5 .

FIG. 10 is a top layout view of a device 1000 that includes an FWD 1010integrated with an Extraction Device 1030 on a single semiconductorsubstrate. The FWD 1010 may be one of the FWDs described above. The FWD1010 is surrounded by a high voltage termination 1020. An ExtractionDevice 1030 is placed outside the high voltage termination 1020 of theFWD 1010. The Extraction Device 1030 includes an input electrode 1032for extraction, an output electrode 1034, and a control electrode 1036.This device 1030 is an example layout of the device 550 of FIG. 5 . Ifthe device 1000 were coupled to a Main Switch, such as an IGBT having anExtraction Plug terminal, the control electrode 1036 would be coupled toa gate of the IGBT, the input (for extraction) electrode 1032 would becoupled to the Extraction Plug terminal of the IGBT, and the outputelectrode 1034 would be coupled to both a collector of the IGBT and to acathode (not illustrated) of the FWD 1010. Finally, the anode (notillustrated) of the FWD 1010 would be coupled to the emitter of theIGBT. When so connected, the FWD 1010 of the device 1000 provides highvoltage protection to the IGBT during turn-off while the ExtractionDevice 1030 substantially increases the turn-off speed of the IGBT.

FIG. 11 is a top layout view of a device 1100 including one or more FWDs1110 and one or more Extraction Devices 1130 as described above. In thislayout, the FWDs 1110 are interleaved with the Extraction Devices 1130in the active area of the die. The electrodes of the Extraction Devices1130 are not illustrated as they may be implementation specific, and maybe placed as the design dictates. Also, the FWDs 1110 illustrated in thedevice 1100 may be coupled together to make one or more FWDs. In otherwords, FWDs 1110A and 1110B may be coupled to one another to make asingle, larger FWD. In another embodiment, all of the FWDs 1110A, 1110B,1110C, and 1110D, maybe be coupled together to make a single FWD for theentire device 1100. The same is true for the Extraction Devices 1130A,1130B, and 1130C, which may be variously connected to one another tomake one, two, or three separate Extraction Devices 1130. FIG. 11illustrates the cellular or tessellated nature of the design in whichmultiple FWDs 1110 and Extraction Devices 1130 may be produced withoutaffecting the functionality of the device. Further, the FWD 1110 andExtraction Device 1130 may be coupled to a one or more IGBTs asdescribed above with reference to FIG. 10 .

FIG. 12 is a top layout view of a complete device 1200 that includes avoltage controlled Main Switch 1210 formed on a first semiconductor diecoupled to an assisting device 1220 formed on a second semiconductordie. The Main Switch 1210 includes Extraction Plugs 700 placed inside anactive area 1250. The active area 1250 of a semiconductor device is thearea within which the main electrical function of the powersemiconductor device is performed. Metallizations 107 connect theExtraction Plugs 700 to each other. A gate terminal 1212 of the MainSwitch 1210 is also illustrated within the active area 1250. The MainSwitch 1210 has its output on the backside of the die. The assistingdevice 1220 includes an FWD 1230 and a PMOS transistor 1240, whichfunctions as an Extraction Device, as described above. The ExtractionDevice 1240 includes an input terminal 1242 for extraction, an outputterminal 1244, and a control terminal 1246.

The Extraction Plugs 700 of the Main Switch 1210 are connected to oneanother through the metalizations 107 and also to the extraction input1242 of the Extraction Device 1240 through a wire bond 1260. A wire bondelectrically connects devices that are produced on two differentsubstrates, where die metallizations cannot be used. Another wire bond1282 couples the gate terminal 1212 of the Main Switch 1210 to thecontrol electrode 1246 of the Extraction Device 1240. With reference toFIG. 5 , the FWD 1230 has its anode coupled to an emitter of the MainSwitch 1210 through a wire bond 1264. The output of the ExtractionDevice 1240 is coupled by a wire bond 1266 to a collector of the MainSwitch 1210, which, as described above, is located on the back side ofthe Main Switch 1210, and is therefore not visible in FIG. 12 . Theoutput of the Extraction Device 1240 is also coupled to the cathode ofthe FWD 1230. This connection between the output of the ExtractionDevice 1240 and the cathode of the FWD 1230 may be an internalmetallization within the assisting device 1220, and is therefore notseparately illustrated in FIG. 12 . Thus, FIG. 12 is an example of aphysical manifestation of the device 560 described above with referenceto FIG. 5 , which includes both a Main Switch 510 and assisting device550. If the complete device 1200 is a three terminal device, then thewire bond 1264 would be coupled to the ground terminal of the device,the wire bond 1266 would be coupled to the output terminal of thedevice, and the wire bond 1262 would be coupled to the control inputterminal of the device. The wire bond 1260 would not need to beconnected to a terminal of the complete device 1200 because theconnection between the Extraction Plug terminal of the Main Switch 1210and the input terminal 1242 of the Extraction Device 1240 need only bean internal connection.

FIG. 13 is a top assembly view of a device 1300 that is similar to thedevice 1200 of FIG. 12 . The same or similar features that weredescribed with reference to FIG. 12 will not be repeated in thedescription of FIG. 13 , for brevity. The main difference betweendevices 1200 and 1300 is that the extraction plugs 700 of the device1300 are formed outside of the high voltage termination 1250, whereasthe Extraction Plugs 700 of the device 1300 are formed within the highvoltage termination 1250. As described above, location of the ExtractionPlugs 700 has little or no effect on their function to provide an accessto the drift area of the semiconductor Main Switch through which theExtraction Device 1240 can expediently remove charge from while the MainSwitch is turning off.

Power semiconductor switches having Extraction Plugs may be developed asa hybrid of the devices 1200 and 1300, with some Extraction Plugs 700located inside the high voltage termination area 1250 and someExtraction Plugs 700 located outside the high voltage termination areawithin the same device itself.

Example Embodiments

In accordance to the present disclosure, an IGBT or other semiconductordevice may take the following forms, along with their equivalents.

Example 1 is a Freewheeling diode integrated with a Forced ExtractionDevice. The Freewheeling diode may be of any kind, such as PIN,Schottky, etc.

Example 2 is a Freewheeling Diode coupled to an Extraction Device,which, in turn, is connected to a Main Switch that includes anExtraction Electrode or Extraction Plugs.

Example 3 is a Freewheeling Diode integrated with an Extraction Device,in which both the Diode and Extraction Device are made on Silicon.

Example 4 is a Freewheeling Diode integrated with an Extraction Device,in which both the Diode and Extraction Device are made on Wide Bandgapsemiconductors.

Example 5 is a Freewheeling Diode integrated with a lateral PMOSExtraction Device, which, in turn, is connected to a Main Switch. Thelateral PMOS Extraction Device has a thick gate oxide that withstands atleast the blocking voltage of the Main Switch (IGBT).

Example 6 is a Freewheeling Diode integrated with a lateral PMOSExtraction Device. The lateral PMOS has a thin gate oxide and a highvoltage rating capacitor that is connected in series with the capacitorof the controlling electrode of the Extraction Device.

Example 7 is a Freewheeling Diode integrated with a vertical PMOSExtraction Device which, in turn, is connected to a Main Switch. Thevertical PMOS Extraction Device has a thick gate oxide that withstandsat least the blocking voltage of the Main Switch (IGBT).

Example 8 is a Freewheeling Diode integrated with a vertical PMOSExtraction Device. The vertical PMOS has a thin gate oxide and a highvoltage rating capacitor that is connected in series with the capacitorof the controlling electrode of the Extraction Device

Example 9 is a High Voltage Capacitor connected in series with thecapacitor of the controlling electrode of the Extraction Device.

The above description of illustrated implementations of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific implementations of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize.

These modifications may be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific implementationsdisclosed in the specification and the claims. Rather, the scope of theinvention is to be determined entirely by the following claims, whichare to be construed in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. A semiconductor device formed on a semiconductorsubstrate, the semiconductor having a first, second, third, and fourthterminals, the semiconductor device comprising: a freewheeling diodecoupled between the first and second terminals; and an Extraction Devicestructured to be coupled to a conductivity modulation switch devicethrough the third terminal, the Extraction Device further coupled to thesecond terminal and the fourth terminal.